gui: treemodel: bail early on empty children updates in IdStringList
gui: treemodel: bail early on empty children updates in IdStringList

SymbiFlow/nextpnr,SymbiFlow/nextpnr,SymbiFlow/nextpnr,SymbiFlow/nextpnr,YosysHQ/nextpnr,YosysHQ/nextpnr,YosysHQ/nextpnr,YosysHQ/nextpnr